4 sub config + 4 extra ceiling subs to cancel height modes (and tangential, oblique modes)???

[Mart Heunen]

Hi all,

I have recently started on making my living room a dedicated listening Room and HT room.

I have four 8" subs, a minidsp, and have tried the half wall and corner configs with relativley same results, which are very nice compared to what i was used to...

However, room height is almost half room length and although from 20hz to 60hz my frequency response and modal ringing have improved, i am having slight trouble with several room modes from 60hz to about 120hz and as far as i have been able to find out they are connected with height modes and very possibly tangential and oblique modes where height is concerned...

So here is my question: Would 4 extra subs on ceiling, in the same config as floor subs config, help with those height/tangential/oblique modes?

Has anyone tried this or have any experience with this in any way?

My room isn't too large (5,1m L, 4,3m W, 2,6m H) and i have 4 8"subs which aren't very powerful but are sufficient for my needs as of yet...

Any help and/or advice is much appreciated!

 

[WaynePflughaupt]

I’m surprised that you were able to get down to 20 Hz with 8” subs.

i am having slight trouble with several room modes from 60hz to about 120hz

How bad are they? If they’re less than 8 db or so, it would be easier to address them with parametric equalization.

Regards,
Wayne A. Pflughaupt

 

[Mart Heunen]

I’m surprised that you were able to get down to 20 Hz with 8” subs.



How bad are they? If they’re less than 8 db or so, it would be easier to address them with parametric equalization.

Regards,
Wayne A. Pflughaupt

Hi Wayne,

thx for your reply...

Maybe i haven't been specific enough and completely honest :s... to be honest my subs are 'rated' for 28hz, but no idea if that's their -10 or -3 specs om paper

I use REW and from 30hz downwards to 15hz i have a slow downward slope, but because of the multiple subs my -10db measurement is approx. 20hz, as in the multisubs help a lot there, where as one sub falls of much more quickly...

With the EQ from the 4way advanced plugin from minidsp i have been able to get the within +/-10db from 60hz to 120hz, but from the top of my head there are like at least 4 room modes, so lots of swings between 60hz and 120hz.... So i guess it's not terrible but i am interested if those ceiling subs would help reduce those modes, cause although EQ in the low frequencies does help a little with 'ringing' i have noticed that 'opposite' subs so to speak do much more for reducing modes and ringing than EQ does...

Hence my question about the extra ceiling subs

 

[KEW]

I doubt it would hurt, but don't know how you would predict the benefit of adding ceiling subs.
Since you have 8" subs, they don't have to be on the floor; I would suggest you experiment with raising a couple of them using chairs/stools, etc. See if you can accomplish what you want without the ceiling subs.

For about 3 years, I had a 12" sealed sub atop a 7' tall cabinet. I was very pleased that it did not set off any audible vibrations, but it was a well built cabinet with good hinges and pads on the doors.

Something like this might get you close enough to validate ceiling mounts and help you optimally locate them.

 

[Mart Heunen]

Hi Kurt,

I have tried raising the subs with chairs and even a couple homemade speakerstands. But so far results are worse than my current config, though i could experiment more and maybe use a cabinet or two as you describe to raise them higher.

Thx for the suggestion.

Still hoping on some answers from people who might actually have tried the 4 floor + 4 ceiling sub setup in any way and could elaborate on those height modes... Maybe just ease my mind and give me the confidence to dive yet deeper in my wallet...

So far i've been getting the essentials and working on 'proof of concept' and watching my budget...
another 4 subwoofers and another minidsp would set me back about 500euro... And i'm not sure if that money is better spent on room treatment or not...

Anyway, thx again for your reply.

 

[WaynePflughaupt]

cause although EQ in the low frequencies does help a little with 'ringing' i have noticed that 'opposite' subs so to speak do much more for reducing modes and ringing than EQ does...

Don’t know what you’ve been using, but parametric EQ is very effective for reducing the ringing of room modes. However, neither EQ nor multiple subs will reduce ringing below what the room normally exhibits. More info on that here.

With the EQ from the 4way advanced plugin from minidsp i have been able to get the within +/-10db from 60hz to 120hz...

A 20 dB deviation in response is actually fairly poor; I would expect one could do better with the miniDSP. Here’s a graph from my subs, accomplished with only four parametric filters. (I don’t worry about anything above ~70 Hz, as response in that range will change once the main speakers are turned on.)

​

another 4 subwoofers and another minidsp would set me back about 500euro...

You wouldn’t need another miniDSP. If you have multiple subs, they should all be equalized in tandem with a single set of filters. After all, that’s the way you hear them – all as a single entity, not as individuals. If you’re EQing them all separately, it never works well. That in itself could account for the problems you’re having.

Still hoping on some answers from people who might actually have tried the 4 floor + 4 ceiling sub setup in any way...

I expect you’ll be waiting a long time. I’ve been participating in a number of home theater forums since 1999, and I’ve never heard of anyone using subs at ceiling level for the reasons you’ve mentioned. The fact that an internet search turns up nothing on the topic should be confirmation enough.

Regards,
Wayne A. Pflughaupt

 

[Mart Heunen]

Eq helps yes, but i find that reducing modes with multiple subs helps better as of yet... in the end i still use eq not only to create a curve but also to 'fix' things and the less i need eq for the latter the happier i would be...

About the deviation you talk about, i might have used it incorrectly... as were my stated claims of my frequency response in the low end... so included is a pic of my freq. response... it looks more like a dev. of +/-5db then, although the max swing is 10db so i am somewhat confused about the terminoligy...

As you can see up to 60hz it's not bad, but from 60hz to about 120hz it's kind of a mess, even after 4 bands of eq for 'fixing' things and 2 bands to 'shape' a desired curve over the whole, then above 120hz i no longer have control of what happens cause i only have the means to do bass managment at the moment.

So i did EQ the subs as a whole, because even though individual eq'ing of subs could help, it's a PITA because of the many phase variances introduced by eq per sub as apposed to the whole.

But that extra minidsp i talked about would come in handy because of individual gain/delay(/phase) control... But i guess it wouldn't strictly be necessary... i mean, none of this is necessary... it's supposed to be fun right? :s

I'm worried that because of my room dimensions i am SOL, hence my question about ceiling subs... But you're probably right and the mighty intrawebs has turned up nothing about this... So maybe i just need to go and do it and report my findings and win a noble prize or something

But my ridiculousness aside, and even though parts of your post i took slightly personal as a kick in the nuts (i'm just doin my best here you know), thank you for your reply and information.

 

[WaynePflughaupt]

...even though parts of your post i took slightly personal as a kick in the nuts...

Ouch (no pun intended). I really should use more smiley faces...

As you can see up to 60hz it's not bad, but from 60hz to about 120hz it's kind of a mess,

That’s really quite good response, even above 60 Hz. IMO you’re fretting to much about what’s going on above 60 Hz. The ripples between 60-70 Hz are probably not audible anyway. If you’re using an 80-90 Hz crossover, any EQ you do in that range is going to be blown out by the main speakers once they’re added to the equation.

Regards,
Wayne A. Pflughaupt

 

[Mart Heunen]

thx again for your reply.

I followed your link and it was a good read.... I have a question though, to check if i understand correctly or if i need to spend more time studying this matter:
Ringing is equally reduced by EQ and mode cancelation (through multiplle subs) because of the gain attenuation factor involved but they both do nothing for decay times??? As in, to truly lower decay times only room treatment wil help, by changing the energie absorbtion of the room for specific frequencies???

 

[WaynePflughaupt]

Ringing is equally reduced by EQ and mode cancelation (through multiplle subs) because of the gain attenuation factor involved but they both do nothing for decay times???

Basically, yes. As the post shows (with graph support), precise parametric EQ can indeed reduce the decay time of a room mode, since it is longer than the decay time the room exhibits. However, the best EQ can accomplish is to bring the mode’s decay time back down to the room’s normal decay time. Reducing decay times beyond that point requires low frequency absorption (aka bass traps).

I don’t know if or how well multiple subs can accomplish the same thing, as I haven’t seen anyone presenting any “before and after” waterfall graphs.

Regards,
Wayne A. Pflughaupt

 

[TheWarrior]

Eq helps yes, but i find that reducing modes with multiple subs helps better as of yet... in the end i still use eq not only to create a curve but also to 'fix' things and the less i need eq for the latter the happier i would be...

About the deviation you talk about, i might have used it incorrectly... as were my stated claims of my frequency response in the low end... so included is a pic of my freq. response... it looks more like a dev. of +/-5db then, although the max swing is 10db so i am somewhat confused about the terminoligy...

View attachment 23252 As you can see up to 60hz it's not bad, but from 60hz to about 120hz it's kind of a mess, even after 4 bands of eq for 'fixing' things and 2 bands to 'shape' a desired curve over the whole, then above 120hz i no longer have control of what happens cause i only have the means to do bass managment at the moment.

So i did EQ the subs as a whole, because even though individual eq'ing of subs could help, it's a PITA because of the many phase variances introduced by eq per sub as apposed to the whole.

But that extra minidsp i talked about would come in handy because of individual gain/delay(/phase) control... But i guess it wouldn't strictly be necessary... i mean, none of this is necessary... it's supposed to be fun right? :s

I'm worried that because of my room dimensions i am SOL, hence my question about ceiling subs... But you're probably right and the mighty intrawebs has turned up nothing about this... So maybe i just need to go and do it and report my findings and win a noble prize or something

But my ridiculousness aside, and even though parts of your post i took slightly personal as a kick in the nuts (i'm just doin my best here you know), thank you for your reply and information.

Running multi subs takes more work, and almost always requires individual EQ and delay settings. But don't let anyone question the size of your subs. A 20 hz sound pressure wave is more than 17 meters in diameter- so feel free to laugh at anyone who thinks an 18" sub (for example) makes a difference in anything but overall SPL output. Dr. Floyd Toole uses 8 inch sealed subs in his room, FWIW.

Need a measurement without any EQ applied and 1/24 octave. Lower resolution measurements can mask the size of resonances.

Need to know any and all inputs you've made including the LFE crossover. Have you adjusted the delay on any of these subs?

We've got room dimensions, but is this room enclosed with a door, or is it open to other rooms? If the latter, going to need LOTS of physical measurements to understand the space that is 'seen' by your sound reproducing equipment.

What are the locations of the subwoofers within the room. And what are distances of those subs to your ears? This is most easily conveyed by drawing a map of your room.

The key to all of this is understanding that you are reproducing frequencies with wavelengths that are larger than the boundaries of the room. This fact is what puts the room firmly in control of which bass frequencies you can hear, at what time, and where, within the room.

Of course this means that you can still influence the sound with positional equalization - think of a subwoofer as a pressure source, if a null is measured at your location it is due to the influence of the room where pressure is at a minimum - DSP can't fix that. If you move the subwoofer closer/further (depending on wavelength) to the listening position, you will see that null vanish.

Peaks can be tamed by DSP, but it is essential to map out ALL of your predicted room modes to know what peaks are actually modes, and what peaks just 'are'. In high resolution measurements, small peaks will exist. But there is a large misconception that in room measurements should resemble flat anechoic measurements. No! Again, your room is in control which means that furnishings and everything else make yours a unique listening experience, otherwise everyone would be posting ruler flat room response graphs. This method is to ensure you hear ALL of the bass at every seat.

Take each physical dimension, multiply by 2, and then divide that number in to 345 m/s - the speed of sound. This will give you the predicted frequency where the boundaries of your room may excite a certain frequency:

Length - 5.1m = 33.8 hz modal frequency (door ways, windows, all can allow boundaries to flex, lowering the modal frequency from prediction, so you start here, and then take acoustic measurements without EQ applied to see what modes are problematic)
2nd Order = 67hz
3rd Order = 100 hz
4th Order = 135 hz - Sound does not bounce off one wall and dissipate, it keeps going until it runs out of energy. Each reflection increases the frequency logarithmically. This information will help you to determine the effectiveness of treating a resonant frequency by seeing its higher order modes dissipate in unison.

Width - 4.3m = 40 hz
2nd = 80hz
3rd = 120hz
4th = 160hz

Height - 2.6m =66.3 hz
2nd = 132 hz
3rd = 199 hz
4th = 265 hz

As you can see, dealing with bass in homes is a rather complex subject that kinda exceeds the limits of internet 'tech support' but I'm trying.

For more information, I strongly recommend 'Sound Reproduction - The Acoustics and Psychoacoustics of Loudspeakers and Rooms' by Floyd Toole. It's a wealth of knowledge that should be sought by anyone who wants to claim audiophile status.

 

[Mart Heunen]

Thx for the write up TheWarrior.

I am a freelance theatre technician with a slight bias towards audio rather than lights, decor and other aspects of the profession. So a lot of the information is already known to me... it's applying it in my own home that is new to me...

I've only played with it for a couple days and the measurment i posted earlier is the best i can do so far...
This was with EQ on all 4 subs as a whole, so no individual EQ, but with some individual delay. I don't smooth my measurments at all at lower frequencies to start with, so the picture i posted is without smoothing... by the way in my posts and the picture you can find some basic info on my config.

As far as i could figure out the 'troubles' i'm having are due to height modes but also tangential modes where height (and length) is concerned and to a lesser extent oblique modes...

I never used multisubs before so when i saw the result between 30hz and 60hz of the first order axial (length and width) modes smoothed out I started wondering about 4 extra ceiling subs to tackle height so to speak... because the frequency response between 30hz and 60hz is as is, no eq applied there, except for a slight room curve over the total bass range, but no heavy peaks or dips there what so ever.

I asked because some knowledge of this specific config or better yet results from someone who has tried it could convince me to try it myself... because i am sort of smart enough to understand the concepts but dont have the means of calculating/predicting results of the specific config i am interested in...

But thank you for your suggestions and yes, Floyd Toole's work is a very good read.

Cheers,

Mart

 

[TheWarrior]

Thx for the write up TheWarrior.

I am a freelance theatre technician with a slight bias towards audio rather than lights, decor and other aspects of the profession. So a lot of the information is already known to me... it's applying it in my own home that is new to me...

I've only played with it for a couple days and the measurment i posted earlier is the best i can do so far...
This was with EQ on all 4 subs as a whole, so no individual EQ, but with some individual delay. I don't smooth my measurments at all at lower frequencies to start with, so the picture i posted is without smoothing... by the way in my posts and the picture you can find some basic info on my config.

As far as i could figure out the 'troubles' i'm having are due to height modes but also tangential modes where height (and length) is concerned and to a lesser extent oblique modes...

I never used multisubs before so when i saw the result between 30hz and 60hz of the first order axial (length and width) modes smoothed out I started wondering about 4 extra ceiling subs to tackle height so to speak... because the frequency response between 30hz and 60hz is as is, no eq applied there, except for a slight room curve over the total bass range, but no heavy peaks or dips there what so ever.

I asked because some knowledge of this specific config or better yet results from someone who has tried it could convince me to try it myself... because i am sort of smart enough to understand the concepts but dont have the means of calculating/predicting results of the specific config i am interested in...

But thank you for your suggestions and yes, Floyd Toole's work is a very good read.

Cheers,

Mart

Ah, then are you familiar with Todd Welti? https://www.harman.com/innovation

That is a link to Harman's 'White papers' which I see has been updated since last I looked. Todd wrote up extensively on incorporating subwoofers from 1 to infinity in to a single room - the element of smoothing bass response from additional subs is what I am referring you to.

But I see Devantier (a friend of Floyd's who showed up at his NRC facility to measure his own loudspeakers as a teen) has added to this section as well. Got some reading to do, myself!

If you are running Windows, try Welti's Resonance program listed further down the page and please report back!

 

[Mart Heunen]

Ah, then are you familiar with Todd Welti? https://www.harman.com/innovation

That is a link to Harman's 'White papers' which I see has been updated since last I looked. Todd wrote up extensively on incorporating subwoofers from 1 to infinity in to a single room - the element of smoothing bass response from additional subs is what I am referring you to.

But I see Devantier (a friend of Floyd's who showed up at his NRC facility to measure his own loudspeakers as a teen) has added to this section as well. Got some reading to do, myself!

If you are running Windows, try Welti's Resonance program listed further down the page and please report back!

Yes Yes i've read 'The white papers' a while back! It was the push i needed to actually buy the extra identical 3 subs... even though they are small and many would say underpowered i am quite happy with the result so far... I first tried the half wall config according to the article but ended up with the 4 corner config cause of spl.
I'll check the artical if i've missed out on some new info...

I've also read tons about room treatment to figure out which ones would benefit my room size the most and budget is somewhat limited as well of course... so first up of are a mix of broadband panels with rockwool (+/-45kg/m3) of 2,3 and 4 inches thick and then i plan to make a few basstraps, but that will be even more trial and error as to the Q and actual frequency of the panels, even though i've read articles about the subject matter (Ethan Winer's work for one, but others as well).

In the end, depending on how i treat my room, that might ultimately limit me in possible sub positioning locations...

I'm on the fence if to go 4 extra ceiling subs and just see what happens, or to first focus on room treatment, because my 'concrete box' could do with some lower decay times.

Anyway, I'll stop rambling now...

Thanks again for your reply!

 

[TheWarrior]

Looking again at your measurements, is your LP nearer the rear wall? I would recommend 4" absorption on the rear wall to limit your front speakers sound reflecting off the rear wall and arriving at your ears near the same time, confusing the sound stage.

From the LP, try placing 2 subs each on the left and right wall 1/3 distance from their adjacent boundaries front and rear. Depending on what DSP you've added, you may want to turn that off to test this new placement. This might mean that the two rear subs are parallel to your seat, which is fine, you will just want to see if there is any cancellation at 40 or 80 hz as a result - in which case apply a filter to one sub to lower its output at that frequency so your seat is not in a null.

One thing you might want to spend more time with from Floyd is discussion of the transition frequency, or Schroeder frequency as you know it. The decay times in most domestic rooms are well with in the desired range for reproduction thanks to the normal furnishings like fluffy pillows, couches, etc. Not trying to talk down to you, just trying to be thorough as I have not seen your baseline measurements.

'Concrete box' suggests you are in a basement or cellar? That presents a whole other set of problems.

If I may, Floyd's work should thoroughly convince you that when it comes sound reproduction in homes, EVERYTHING matters.

You've peaked my interest and if you would like to keep discussing on forum or privately, awesome! Add some pics in and give me everything and we'll see if we can't at least get you some orientation to go forth, with!

 

[Mart Heunen]

My LP is approx. 40% (+/-2m) from rear wall... So yes, i am planning absorption on rear wall instead of diffusion or a combo. My measurments have not been very extensive but so far the center of the room is a no go. Further to front wall seems ok and helps with spl, but the room is only 5m length and my TV is 60" so it gets 'big' really fast, if you know what i mean... also legroom starts to diminish and overall livingroom comfy/feely-ness starts to degrade.

I don't quite understand your 2 sub 1/3 placement suggestion:

I made a top down view in paint of my current setup and two (1 and 2) possible setups the way i think you might have meant your suggestion.

About decay times, this all btw is from the top of my head because i didnt save previous data:
The decay times above the schroeder frequency, which was somewhere between 175 and 225hz for my room IIRC, are approx. 350ms downwards to 250ms in the upper frequencies from about 80db to my rooms lowest noisefloor of 45db, so not great but not my biggest worry as of yet... It's the decay times of the low frequencies i'd like to tackle.

Then after that, or in combo with that as prioritisation goes, first reflections. So i'm planning on membrane traps fixed on side walls and ceiling and a couple seperate ones near front and back wall. And then see how things look on paper a.k.a computer, but also how it sounds to me and if i'm happy i'll stop there... but... knowing myself i'll keep going and trying to improve until i really can't justify pouring any more money into it.... Mind you i'm not talking about tens of thousands of euros... so far including equipment, speakers (including center and surrounds), subs, cables and the few broadband absorbers i've made, i'm in it for about 2000euros and it's by no means the best equipment out there, but i have to spread my budget you know... So with the membrane traps and possibly later with extra broadband panels , i might sink in another 1000, 2000 tops....
I'm not even planning on using my room professionaly... just for fun.

Concrete box: no, no basement or cellar, but i live in an appartment and floor, ceiling and side walls are reinforced concrete... yikes (see my awesome drawing for 'more details'

Thank you for your suggestion and if you get back to me on that i 'll give it a go and post results...
Any other things worth writing down and mentioning? let me know!
Thank you for your interest and time... It makes this journey that extra bit of fun.

 

[TheWarrior]

The recommended screen size vs distance ratio is 1.2 - 1.6. You're at a 2, so if a more immersive viewing experience is of interest, move closer. Even a small adjustment forward might improve viewing and listening...

1/3 placement: Starting on the right side of the room in the corner with the cupboard - place one sub 1.6 meters from that cupboard, and place the other sub 3.4 meters away. For the left side, adjust for the shorter dimension, this does not need to be a mirror image, controlling the pressure in the room in relation to the boundary is what matters; And this is my response to your beautifully proposed arrangements.

Decay times - those are not bad, and knowing that you are going to add absorption means we know they will improve anyway, so lets not worry about those.

With that low of a noise floor, you must get treated to excellent dynamic range! My home has very thin stud walls in close proximity to a busy road so I'm a bit higher than you, there!

The thing about cement is that it (obviously) is providing you very good sound insulation, except that it is not very forgiving to smaller wavelengths. I would add absorption slowly to tame any bass issues, and for the rear wall. The glass at the front is certainly a problem, and I hope you have a dense curtain you can pull over it, at least. But my concern is cement wall + too much absorption = dead room.

If you do not have a good cover/curtain for the window, I would do that next. First reflections are absorbed in mastering rooms, but they greatly contribute to perceived LEV (listener envelopment) and ASW (apparent source width) per Floyd Toole. I would consider this last, as you may be pleased with the sound after all the other absorption is added, first.

Lets consider some other options before spending money on membrane traps... don't forget, a couch is an absorber too!
http://www.gikacoustics.com/product/evolution-polyfusor-diffusor-absorber-bass-trap/
These offer the best of both worlds.

A combination of those with rear wall absorption would be a great start. I don't know where you live, but I figure GIK Acoustics might be something available to you. I have several of their products including the ArtPanels - dye sublimation printing of images - highly recommended!

My pursuit of audio heaven has actually led me to take a 'crash course' in electrical engineering and am working on a new center channel speaker which I hope to turn in to a full front L/C/R arrangement later on. And of course reading either 2nd or 3rd edition of Floyd's 'Sound Reproduction' will always keep my mind racing. Not sure yet what I am going to do with all of this knowledge, but I am sure it will sound good!

 

[Mart Heunen]

Sub placement suggestion - Ah thx... i think i get it. Will try soon and report back.

Screen size/viewing distance ratio - I'm actually just over 1.6 for screen size vs viewing distance ratio, because the TV is on a tv stand pulled slightly into the room... But yes a bit closer does increase immersion, so i might be able to pull the TV closer but it's also a trade of with it still being a living room and having room to maneuver and such
So sitting in the 'first half' of the room is just a bit to close, and i'd also like to avoid the middle of the room... but who knows, in the end with all the measurments and adjustments done it might be "the" spot.

Decay times - those i stated were for higher frequencies... i just did a measurment and below 100hz they are really bad IMO with some modes over 700ms.
So it'll be finding a balance of low freq absorption with panels but not to deaden the room in higher frequencies.... i'll do adjustments in small steps.

Oh and thx for the GIK suggestion... too steep a price though for how many i would probably need for my liking... I'm going DIY, even if it means not knowing the actual precise specs/results of the membrane panels i am going to build. I just hope their Q will be in the ballpark of 1/2 to 1 octave so that being slightly off with the center frequency wont matter to much.

- Interesting point about the first reflections! I'll keep it in mind and focus on bass trapping and back wall first and then experiment later with first reflections... though i just might still do it... my walls are really really hard and reflect everything, oh and did i mention my walls are slightly slant as well :s... terrible flutter echo...

Noise floor: i said 'my lowest' noisefloor was 45db so that's when it's dead quiet everywhere around my appartment... otherwise it's usually around 50db pushing 52/53 at times... And maybe due to concrete it's especially the low frequencies that contribute to this... they are approx 5db louder than higher frequency noise floor.. but maybe this is normal due to high reflection outside but low freq seaping through so to speak... quite new to me because in pop venues and/or theaters the noise floor is a bit more evenly spaced over all frequencies...

Curtain - yes i have one, but since the glass is on the front wall it's mostly low frequencies that pose a problem there i think, maybe even the glass is resonating to low frequencies and causing terrible decay times... i could try and make some broadband panels on rails (like curtains) there so i can still open them so i don't completely turn into a vampire...

Electrical engineering - That is very cool to hear! for me it's a bit the other way around:
my grandpa had a hardware store and was an electrician, and so my father was as well for a while and he dabbled in building speakers, though not making his own filters... He recently gave me all his left overs and there were some old philips speakers as well as a lot of visaton stuff...
It peaked my interest and i started catching up on mathmatical formulas as to how filters work and such but the learning curve was just a bit to steap for me and i had to prioritize some things...

I hope your endeavour goes well! Are you keeping records like say a build log or anything? if so, send me a link and i can check on it once in a while.

cheers,

Mart

 

[TheWarrior]

Tell me more about this membrane absorber you are building. How thick is it, what is it made of, and where are they going to be placed in the room? Only one octave of bandwidth seems rather narrow for a membrane absorber, doesn't it?

But yeah, you've got it, just add absorption in stages. Surely you've been in an over-damped control room where it is uncomfortable, even to have a conversation?

Curtains - thick curtains do well, and if you add a valance you can hide thicker absorption behind it, and achieve broad band absorption much more easily, with no rails or panels to deal with.

Very interesting, so you had an EE in the family, your father followed suit and dabbled in speakers, and you went with sound production in theaters? Do you have children? Do they know what they have to live up to!? Haha!

My story is quite different. No engineers, my family is in marketing and public relations for home building products, particularly plumbing. American Standard once held, "It's seen you naked, it's heard you sing." as their tag line - that was my Dad.

I always loved music, but I never had any musical influences. Sold my saxophone to get my first stereo and have been obsessed ever since. Moved to CA on the the BMW in my picture to be with a woman, and got hit by a car. I was learning to cook and wanted to have a restaurant that would just have me cranking out food for the people all day, everyday. Can't physically do that anymore, so I turned to books and wood working. Then I discovered Floyd Toole. Now I am preparing to build my first loudspeaker that I will test in accordance with a measurement standard Floyd and his team at Harman helped create.

Hoping to have a completed enclosure and crossover by March so I can test it outdoors. I don't have a website, but I do have a thread in the 'Pros n Joes' subforum called 'Custom Self Built Theater'. My photo hosting is down so there are no pics, currently, but as I am renovating my home, there will be some major changes coming.... so stick around!

 

[yepimonfire]

The recommended screen size vs distance ratio is 1.2 - 1.6. You're at a 2, so if a more immersive viewing experience is of interest, move closer. Even a small adjustment forward might improve viewing and listening...

1/3 placement: Starting on the right side of the room in the corner with the cupboard - place one sub 1.6 meters from that cupboard, and place the other sub 3.4 meters away. For the left side, adjust for the shorter dimension, this does not need to be a mirror image, controlling the pressure in the room in relation to the boundary is what matters; And this is my response to your beautifully proposed arrangements.

Decay times - those are not bad, and knowing that you are going to add absorption means we know they will improve anyway, so lets not worry about those.

With that low of a noise floor, you must get treated to excellent dynamic range! My home has very thin stud walls in close proximity to a busy road so I'm a bit higher than you, there!

The thing about cement is that it (obviously) is providing you very good sound insulation, except that it is not very forgiving to smaller wavelengths. I would add absorption slowly to tame any bass issues, and for the rear wall. The glass at the front is certainly a problem, and I hope you have a dense curtain you can pull over it, at least. But my concern is cement wall + too much absorption = dead room.

If you do not have a good cover/curtain for the window, I would do that next. First reflections are absorbed in mastering rooms, but they greatly contribute to perceived LEV (listener envelopment) and ASW (apparent source width) per Floyd Toole. I would consider this last, as you may be pleased with the sound after all the other absorption is added, first.

Lets consider some other options before spending money on membrane traps... don't forget, a couch is an absorber too!
http://www.gikacoustics.com/product/evolution-polyfusor-diffusor-absorber-bass-trap/
These offer the best of both worlds.

A combination of those with rear wall absorption would be a great start. I don't know where you live, but I figure GIK Acoustics might be something available to you. I have several of their products including the ArtPanels - dye sublimation printing of images - highly recommended!

My pursuit of audio heaven has actually led me to take a 'crash course' in electrical engineering and am working on a new center channel speaker which I hope to turn in to a full front L/C/R arrangement later on. And of course reading either 2nd or 3rd edition of Floyd's 'Sound Reproduction' will always keep my mind racing. Not sure yet what I am going to do with all of this knowledge, but I am sure it will sound good!

Whether or not to absorb or diffuse first reflections is a matter of the time of arrival. In my case, my speakers are fairly close the the left and right walls. Impulse response measurements show that the reflections from the side walls are delayed by only 2ms, which is short enough and loud enough to cause the haas effect to break down. Without absorption, stereo imaging is smeared and incoherent, with absorption it sounds so much better. Contrary to popular belief, toole has never stated that early reflections are always ideal and should be left untreated. It really depends on the room and purpose of the setup. If the direct sound is significantly louder than the reflected sound, and the reflected sound is sufficiently delayed, absorption may not be needed.

I currently use Auralex 2” wedgies for HF reflection absorption. They’re effective down to about 500hz, and they actually work better than something like 2” rigid fiberglass. A steep angle of incidence, as is often seen with side wall/ceiling reflections is a problem with flat absorbers in small rooms. The multiple angles of the wedge design of the Auralex solves this problem. For problems below 500hz, I just use eq. Bass traps can certainly help, but the size required or distance from the wall must be 1/4 wavelength of the lowest frequency one is trying to absorb. Even at 50hz, this is about 5 feet. Multiple, carefully placed subs and eq is more practical.